The city shall make contributions to provide prior service and widow's prior service annuities, and other annuities and benefits, as follows:
Provided that if in any year such total sums together with all other sums required during such year for the other purposes of the fund, are in excess of the total amount contributed by the city during such year, the sums required for purposes other than those stated in this Section shall first be provided for. The balance shall then be applied for the purposes stated in this Section.
All such contributions shall be credited to the prior service annuity reserve. When the balance of this reserve equals its liabilities (including in addition to all other liabilities, the present values of all annuities, present or prospective, according to the applicable mortality tables and rates of interest, but excluding any liabilities arising under Sections 11-133.3 and 11-133.4), the city shall cease to contribute the sum stated in this Section.
If annexation of territory and the employment by the city of any person employed as a city laborer in any such territory at the time of annexation, after the city has ceased to contribute as herein provided, results in additional liabilities for prior service annuity and widow's prior service annuity for any such employee, contributions by the city for such purposes shall be resumed.
Notwithstanding any provision in this Section to the contrary, the city shall not make a contribution for credit established by an employee under subsection (b) of Section 11-133.3.
40 ILCS 5/11-178